HiddenSave automatically saves every message to your hard disk before it is sent out. The saved Message File has an .msg Extension, so simply double click the .msg File to open it again in Outlook.
With this you can ensure that for example every outgoing message is stored for archiving purposes in case the message accidentially gets lost (deleted) in Outlook.
The best thing is that you will not even notice that HiddenSave is active. No additional buttons or menu items are being displayed.